At present, video, music, and other digital content are distributed on DVDs or other playback-only optical discs (see, for example, non-patent document 1). In a new form of content distribution now under study, a content provider places content in a server, users who wish to purchase the content access the server through a communication means such as the Internet, and the purchased content is downloaded through the communication means to a user terminal and recorded on a recording medium such as a DVD-R at the user terminal. In some exemplary DVD cases, the disc on which the downloaded content is recorded can be reproduced by a DVD player (see, for example non-patent document 2).
Streaming and downloading distribution systems for viewing or listening to content placed on a server by accessing the server through communication means are already in use. In these distribution systems, the user can view or listen to the distributed content freely up to a number of times agreed to in a contract at the time of purchase of the content, or during a contracted period of time (see, for example patent document 1). However, the content can only be reproduced on a dedicated reproduction system; it cannot be recorded and saved onto a removable medium such as an optical disc, and the user cannot view or listen to the content free of time period restrictions or playback count restrictions.
To compare the former with the latter, that is, to compare the download recording of content onto an optical disc with the streaming distribution or download distribution of the content, when the user views or listens to the content, in the latter case the user can generally perform only simple operations on the content, such as fast-forward, rewind, slow play, and pause.
In the former case, the content downloaded and recorded on the disc is identical to authored content provided on playback-only optical discs, so the same elaborate user interface can be used as for content distributed on playback-only optical discs. For example, in playback-only DVD-Video, the content may be divided into chapters, and a list of images representing the chapters may be displayed on a menu screen from which the user can select what to reproduce, or the user may be able to select one of several languages or subtitles, or conduct various other operations by using a remote control to select buttons displayed on the screen. It would be desirable for content downloaded and recorded on a disc to have equivalent functionality and convenience.
Together with convenience, copyright protection of content is also important, and functions for preventing illegal copying are also now under study. In both of the methods described above, however, copyright protection is focused on enhanced encryption or enhanced encryption management (see patent document 2, for example); no method of preventing illegal copying by a combination of the data structure of the content and the disc structure has been presented so far.    Patent document 1: PCT Patent Application, Japanese-language Publication No. 2004-507124    Patent document 2: Japanese Patent Application Publication No. 2004-350150    Non-patent document 1: Standard ECMA-267, ECMA, 2001, pp. 32-37    Non-patent document 2: Toshiba Review, Vol. 60, No. 2, pp. 50-53, 2005